Modular phantom for assessment of imaging performance and dose in cone-beam CT

ABSTRACT

Embodiments provide a modular phantom that enables quantitative assessment of imaging performance (e.g., spatial resolution, image uniformity, image noise, contrast to noise ratio, cone-beam artifact) and dosimetry in cone-beam computed tomography (CT). The modular phantom includes one or more modules for various imaging performance tests that may be rearranged in the phantom to accommodate the design of various cone-beam CT imaging systems. The modular phantom includes one or more of a cone-beam module, an angled edge module, or a line spread module. The phantom may be inserted into a larger sleeve and be used to assess imaging performance and dosimetry in whole body CT imaging systems.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2019/039977 filed Jun. 28, 2019, which claims benefit under 35 USC§ 119(e) to U.S. Provisional Patent Application No. 62/692,574 filedJun. 29, 2018, the disclosures of each which are incorporated byreference herein in their entireties for all purposes.

BACKGROUND

A medical imaging phantom is an object that is scanned or imaged toevaluate, analyze, and tune the performance of various imaging devices.A phantom provides more consistent results than the use of a livingsubject or cadaver, and avoids subjecting a living subject to repeatedradiation exposure. Phantoms were originally employed for use in 2DX-ray-based imaging techniques such as radiography or fluoroscopy,though more recently phantoms with desired imaging characteristics havebeen developed for 3D techniques such as magnetic resonance imaging(MRI), computed tomography (CT), ultrasound, positron emissiontomography (PET), and other imaging methods or modalities.

Existing medical imaging phantoms typically involve complex designs toenable subjective, qualitative assessment of image qualitycharacteristics of a medical imaging device. Conventional phantoms arenot capable of measuring the imaging performance and the dosimetry.Moreover, existing phantoms do not cover a range of imaging performancemeasurements and are not generally configurable in a manner suitable toa broad range of cone-beam CT scanner configurations. In addition,conventional phantoms are inconsistent with emerging standards forphysical measurements for cone-beam CT accreditation in a number ofways, including overall dimensions (diameter and length) and in terms ofincluding of test objects which permit the required measurementsincluding conventional measurements and those specifically useful incone-beam CT.

Embodiments address these and other technical problems, individually andcollectively.

SUMMARY

Embodiments provide a modular phantom that enables quantitativeassessment of imaging performance and dosimetry (i.e., measurement andassessment of ionizing radiation exposure levels delivered to thephantom during imaging) in cone-beam computed tomography (CT). Thephantom includes one or more interchangeable and rearrangeable modules.The phantom provides a common, combined device for assessing imagingperformance (for example, via the modules) and radiation dosimetry (forexample, via one or more bore holes provided in the modules toaccommodate the placement of an instrument at one or more positions inthe modules).

The phantom discussed herein reflects an important design principle thatstresses simplicity in physical design while emphasizing quantitativeanalysis which produces a number quantitative metrics which define imagequality. The phantom according to various embodiments allows measurementof imaging performance and dosimetry within the same imaging system,using the same technique factors of the imaging system. According tovarious embodiments, the technique factors may include one or more of atube potential (measured in kilovoltage (kV)), a tube current (measuredin milliamperage (mA)), a time of exposure, and a system geometry of theimaging system (e.g., a field of view (FOV) of the imaging system, asource-axis-distance (SAD) of the imaging system, asource-detector-distance (SDD) (also called as a source-imager-distance(SID)), and an extent of the source-detector orbit) of the medicalimaging device).

Embodiments provide a modular phantom for medical imaging and dosimetrycomprising one or more modules ordered according to a predeterminedorder. The one or more modules include at least one of a cone-beammodule configured to measure a cone-beam artifact for a medical imagingsystem, an angled edge module configured to measure at least one of aspatial resolution or contrast properties of the medical imaging system,or a line spread module configured to measure a line-spread function ofthe medical imaging system. The modular phantom is configured to measurean imaging performance of the medical imaging system including themodular phantom and a dosimetry of the medical imaging system. In someembodiments, the modular phantom may include a sleeve configured toenvelop the one or more modules. The modular phantom may include atleast one homogenous module.

In some embodiments, the modular phantom comprises two or more modules,and attachment means for attaching the two or more modules. Theattachments means align the two or more modules. The attachment meansinclude at least one supporting rod. Each module includes at least onethrough hole extending through the module, and through holes through aplurality of modules are aligned for receiving the at least onesupporting rod.

In some embodiments, the imaging performance and the dosimetry of themedical imaging system are measured using a same set of techniquefactors for the imaging system. The set of technique factors include oneor more of a tube potential, a tube current, a time of exposure, and asystem geometry of the imaging system (e.g., a field of view (FOV) ofthe imaging system, a source-axis-distance (SAD) of the imaging system,a source-detector-distance (SDD), and an extent of the source-detectororbit) of the medical imaging device).

According to various embodiments, the modular phantom may include one ormore through holes configured to receive one or more instruments formeasuring the dosimetry of the medical imaging system. The one or moreinstruments include an ionization chamber.

In some embodiments, the modular phantom may include two or more of thesame module. The modular phantom may include a first cone-beam moduleprovided along a central axial plane of the modular phantom where a coneangle is zero, and a second cone-beam module provided at a predetermineddistance of the central axial plane of the modular phantom where thecone angle is not zero. The predetermined distance of the central axialplane of the modular phantom is greater than 1 cm.

In some embodiments, at least one of the one or more modules includes acavity adapted to receive an insert based on a medical imaging anddosimetry application associated with the modular phantom. The insertand a module comprising the insert are made of different materials. Thecone-beam module includes at least one cavity, and an insert provided inthe at least one cavity. The insert for the cone-beam module includes atleast two components stacked along a z-direction of the cone-beammodule. The angled edge module includes at least one cavity, and aninsert provided in the at least one cavity. The insert for the anglededge module has at least one angled edge. The line spread moduleincludes at least one cavity, and an insert provided in the at least onecavity. The insert for the line spread module includes a slit extendingalong a central line of the insert.

Embodiments also provide a medical imaging system comprising a radiationsource configured to emit x-rays, a detector, and a modular phantomplaced between the radiation source and the detector. The modularphantom includes one or more modules ordered according to apredetermined order, the one or more modules including at least one of acone-beam module configured to measure a cone-beam artifact for themedical imaging system, an angled edge module configured to measure atleast one of a spatial resolution or contrast properties of the medicalimaging system, or a line spread module configured to measure aline-spread function of the medical imaging system. The x-rays emittedfrom the radiation source travel through the modular phantom beforebeing received at the detector.

Embodiments further provide a method for measuring properties associatedwith a medical imaging system using a modular phantom including one ormore modules ordered according to a predetermined order, the one or moremodules including at least one of a cone-beam module configured tomeasure a cone-beam artifact for the medical imaging system, an anglededge module configured to measure at least one of a spatial resolutionor contrast properties of the medical imaging system, or a line spreadmodule configured to measure a line-spread function of the medicalimaging system. The method includes determining one or more propertiesassociated with an imaging performance of the medical imaging system tobe measured. The method further includes identifying the predeterminedorder of the one or more modules based on the one or more properties tobe measured. The method includes assembling the modular phantom based onthe predetermined order; and placing the modular phantom between adetector and a radiation source of the medical imaging system. Themethod also includes collecting a first set of rays that are emittedfrom the radiation source on the detector after the rays travel throughthe modular phantom. The method further includes measuring the one ormore properties associated with the imaging performance of the medicalimaging system using the collected first set of rays; and measuringdosimetry of the medical imaging system using the collected first set ofrays. Measuring the one or more properties associated with the imagingperformance of the medical imaging system may further include measuringone or more of a spatial resolution, an image uniformity, an imagenoise, a contrast, a contrast to noise ratio, or the cone-beam artifacton the image acquired using the medical imaging system. In someembodiments, the method may include aligning at least one of the one ormore modules with a central ray of the medical imaging system.

According to various embodiments, the method may also include removingthe modular phantom from the medical imaging system; and assembling themodular phantom based on a different predetermined order into a modifiedmodular phantom. The modified modular phantom may be placed between thedetector and the radiation source of the medical imaging system. Themethod may further include collecting a second set of rays that areemitted from the radiation source on the detector after the rays travelthrough the modified modular phantom. The one or more propertiesassociated with the imaging performance of the medical imaging system ismeasured using the collected second set of rays. The dosimetry of themedical imaging system is measured using the collected second set ofrays.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed description purports to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a perspective view of an exemplary assembled modularphantom in accordance with embodiments of the invention;

FIG. 1B illustrates a top or bottom view of an exemplary assembledmodular phantom in accordance with embodiments of the invention inaccordance with embodiments of the invention;

FIG. 1C illustrates a side view of an exemplary assembled modularphantom in accordance with embodiments of the invention in accordancewith embodiments of the invention;

FIGS. 1D-1E illustrate exemplary attachment means for adjacent modulesof a modular phantom in accordance with embodiments of the invention;

FIGS. 2A-2B illustrate an exemplary sleeve for the modular phantom inaccordance with embodiments of the invention;

FIG. 3A illustrates a perspective view of a cone-beam module inaccordance with embodiments of the invention.

FIG. 3B illustrates a top view and corresponding cut-out views of acone-beam module in accordance with embodiments of the invention.

FIG. 3C illustrates a side view of a cone-beam module in accordance withembodiments of the invention.

FIG. 3D illustrates an exemplary cone-beam module, excluding holes forsupport rods and dosimetry in accordance with embodiments of theinvention.

FIG. 3E illustrates an image of the cone-beam module of FIG. 3D capturedin a tomographic plane (for example, a coronal or sagittal slice)perpendicular to the plane of the disks of the insert in accordance withembodiments of the invention.

FIG. 3F illustrates an exemplary profile of pixel values correspondingto the axis illustrated in FIG. 3E.

FIG. 3G illustrates a perspective view of an exemplary cone-beam moduleinsert in accordance with embodiments of the invention.

FIG. 3H illustrates a perspective view of components of an exemplarycone-beam module insert in accordance with embodiments of the invention.

FIG. 3I illustrates a top or bottom view of an exemplary cone-beammodule insert in accordance with embodiments of the invention.

FIG. 3J illustrates a side view of an exemplary cone-beam module insertin accordance with embodiments of the invention.

FIG. 4A illustrates exemplary angled edge module and inserts inaccordance with embodiments of the invention.

FIGS. 4B-4D illustrate cross-sectional views of an exemplary modularphantom including an angled edge module in accordance with embodimentsof the invention.

FIGS. 4E-4H illustrate exemplary angle edge modules with various typesand number of inserts in accordance with embodiments of the invention.

FIG. 5A illustrates a perspective view of exemplary line spread modulein accordance with embodiments of the invention.

FIG. 5B illustrates a top/bottom view of a line spread module inaccordance with embodiments of the invention.

FIG. 5C illustrates a side view of a line spread module in accordancewith embodiments of the invention.

FIGS. 5D-5E illustrate exemplary insert components for a line spreadmodule in accordance with embodiments of the invention.

FIG. 6A illustrates a perspective view exemplary uniform module inaccordance with embodiments of the invention.

FIG. 6B illustrates a side view of a uniform module in accordance withembodiments of the invention.

FIG. 7A illustrates an exemplary phantom with one or more radiationmeasurement instruments inserted in the through-holes in accordance withembodiments of the invention.

FIGS. 7B-7C illustrate an exemplary phantom aligned with a medicalimaging system in accordance with embodiments of the invention.

FIG. 8 illustrates a flowchart of steps for measuring the imagingperformance and dosimetry of the medical imaging system in accordancewith embodiments of the invention.

FIG. 9 illustrates shows an exemplary computer system, in accordancewith embodiments of the present invention

DETAILED DESCRIPTION

Modular Phantom Design

Embodiments provide a modular phantom that enables quantitativeassessment of imaging performance (e.g., noise, noise variance, or noisepower spectrum) of one or more medical images (e.g., a scan) acquiredusing a medical imaging system and dosimetry meter associated with themedical imaging system. For example, the medical imaging system mayinclude a cone-beam computed tomography (CT) scanner or a whole-body CTscanner. The quantitative assessment of the imaging performance and thedosimetry associated with the imaging system may be accomplished usingthe same technique factors (e.g., a tube potential (measured inkilovoltage (kV)), a tube current (measured in milliamperage (mA)), atime of exposure, and a system geometry of the imaging system (e.g., afield of view (FOV) of the imaging system, a source-axis-distance (SAD)of the imaging system, a source-detector-distance (SDD) (also called asa source-imager-distance (SID)), and an extent of the source-detectororbit)) of the medical imaging device.

In some embodiments, the modular phantom may be sized and dimensionedbased on the particular use or medical imaging system. For example, themodular phantom may be inserted in a sleeve. The sleeve may have anyshape (e.g., a circular or elliptical annulus) with a hollow cavity forreceiving the modular phantom therein. Accordingly, the interior portionof the resulting assembly containing the modular phantom may be smallerthan the exterior portion of the assembly for the quantitativeassessment of the imaging performance and the dosimetry associated withlarger body sites or sizes. The sleeve may be configured to increase thediameter of the phantom (e.g. bulk up the phantom) to a diameter largerthan the diameter of the various modules.

As used herein, a phantom may include a test object for medical imagingand dosimetry. The dosimetry may refer to the measurement, calculationand assessment of the ionizing radiation dose absorbed by the testobject. According to various embodiments, the phantom may be a modularphantom including one or more modules. The one or more modules forvarious imaging performance tests may be rearranged in the modularphantom to accommodate the design of various medical imaging systemsincluding, but not limited to, cone-beam CT systems. According tovarious embodiments, the phantom may be adapted to a variety ofcone-beam CT imaging applications, including dental imaging,ear-nose-throat (ENT) imaging, orthopedic imaging, breast imaging, andinterventional C-arms.

The modules for measuring the imaging performance of the medical imagingsystem include test objects suitable to assessment of spatial resolutionin three spatial dimensions, image uniformity, image noise, contrast,contrast to noise ratio, and cone-beam artifact as well as radiationdose. The modules may also enable measurements that are consistent withemerging standards for physical measurements in cone-beam CTaccreditation.

As used herein, spatial resolution may include the cut-off or Nyquistresolution that may refer to the smallest feature that can bedistinguished in an image. The spatial resolution defined by themodulation transfer function (MTF) describes how well objects ofdifferent size can be seen. The MTF is commonly characterized in termsof the point-spread function (PSF), line-spread function (LSF), oredge-spread function (ESF). A separate MTF can be computed for eachspatial direction (i.e., x, y, or z), or 2D and 3D MTFs can be computedcombining directions.

As used herein, image uniformity may refer to the degree to which thesignal in the image of a uniform, homogeneous object (e.g., a cylinderof water) is uniform (i.e., constant) throughout the object. Incone-beam CT, effects such as x-ray scatter, beam-hardening, andcone-beam effects may reduce the image uniformity.

As used herein, image noise may refer to fluctuations in the image thatdo not correspond to true variations associated with the object. Theimage noise arises from stochastic effects such as x-ray quantum noiseor electronic readout noise. The image noise is commonly characterizedin terms of the standard deviation of image values (within an otherwisehomogeneous region of an object) and/or the noise-power spectrum (NPS)which characterizes not only the amplitude of the noise, but also thefrequency dependence or “texture” of the noise.

As used herein, image contrast may refer to the difference in meansignal value between two regions (e.g., adjacent regions) in an image.For example, contrast may refer to the difference in image array scalebetween a region of acrylic and a region of polyethylene.

As used herein, contrast-to-noise ratio (CNR) is given by the imagecontrast (defined above) divided by the noise (defined above).

As used herein, the cone-beam artifact refers to a visual feature thatappears on an image (acquired using a cone-beam CT scanner) of an objectthat is not present in the original object. That is, the cone-beamartifact may refer to an error in an image acquired with a particularimaging system. The cone-beam artifact may typically arise from 3D imagereconstruction from data acquired in a circular orbit of a divergent(“cone”) beam of x-rays and an area detector. The cone-beam artifact maybe induced by discrepancies between the mathematical modeling and theactual physical imaging process. The presence of the cone-beam artifactin the acquired image may degrade the quality of the image to anon-diagnostic level.

Embodiments provide one or more modules that are configured to detect ormeasure one or more of the imaging performance elements of the medicalimaging system as described above. The one or more modules include acone-beam module configured to measure the cone-beam artifact generated(e.g. caused) by the medical imaging system, an angled edge moduleconfigured to measure at least one of a spatial resolution or thecontrast properties of the medical imaging system, and a line spreadmodule configured to measure the line-spread function of the medicalimaging system. The line spread module may contain one or more slitswith different slit widths, to accommodate CT systems with differentresolving power.

According to various embodiments, the phantom may include two or more ofthe same (or nearly identical copies of) module. The modules may berearranged along the length (e.g., in z-direction) of the phantom,depending on the needs of the assessment. According to variousembodiments, the phantom may include any of the modules, (e.g., acone-beam module configured to measure a cone-beam artifact for amedical imaging system, an angled edge module configured to measurespatial resolution and/or contrast properties of the medical imagingsystem, or a line spread module configured to measure a line-spreadfunction of the medical imaging system), in any order along the longaxis of the phantom. The modules are described below in greater detail.

FIG. 1A illustrates a perspective view of an exemplary modular phantom100 that includes a plurality of modules such as a uniform module 110, acone-beam module 120, a line spread module 140, and an angled edgemodule 170. According to various embodiments, the modular phantom 100may include more or less modules. In some embodiments, the modularphantom 100 may include a single module, while in other embodiments themodular phantom 100 may include multiple modules. The exemplary modularphantom 100 illustrated in FIG. 1A also includes more than one of thesame module, such as the uniform modules 110′, and the cone-beam module120′. FIG. 1B illustrates the top view of the modular phantom 100 andFIG. 1C illustrates a side view thereof. According to variousembodiments, the modular phantom 100 may be coupled to a medical imagingsystem, and may be configured to measure an imaging performance and adosimetry of the medical imaging system using a same set of techniquefactors (e.g. a tube potential, a tube current, a time of exposure, anda system geometry (e.g., a field of view (FOV) of the imaging system, asource-axis-distance (SAD) of the imaging system, asource-detector-distance (SDD), and an extent of the source-detectororbit of the medical imaging system).

The modules of the modular phantom 100 may be ordered according to apredetermined order. The predetermined order of the modules in themodular phantom 100 may depend on the use of the phantom. For example,the modular phantom 100 may include the line spread module 140 alignedwith the central ray of a CT scanner to optimize the evaluation ofspatial resolution in the (x, y) plane of the imaging system. Thecentral ray of an imaging system may refer to the ray containing thex-ray source and intersecting the detector at a right angle. In someembodiments, the modules may be removed from the modular phantom 100 andreordered before being assembled again in form of the modular phantom.The order of the modules within the modular phantom 100 is discussedbelow in greater detail.

It may also be necessary to include more than one of the same module inthe modular phantom depending on the desired measurements to beperformed using the modular phantom. For example, a first cone-beammodule may be provided along a central axial plane of the modularphantom where a cone angle is zero (i.e. the first cone-beam module isplaced in the plane of the x-ray source), and a second cone-beam modulemay be provided at a predetermined distance (e.g., greater than 1 cm) ofthe central axial plane of the modular phantom where the cone angle isgreater than or less than zero (i.e. the second cone-beam module isplaced at the predetermined distance from the plane of the x-ray source,such as near the end of the field of view along the z-axis).

The modules of the modular phantom 100 may be kept together using anytype of attachment means including but not limited to fasteners, supportrods, removable adhesives, a sleeve covering the modular phantom, etc.Different type of attachment means may be used together. For example,the modular phantom may include one or more support rods, and may beinserted into a sleeve. The attachment means may be used to keep themodules together. The attachment means may also align the modules, ifrequired for the particular use of the modular phantom.

For example, the modules of a modular phantom may be held together usingone or more support rods 160, as illustrated in FIG. 1A. The supportrods 160 can be inserted into through holes (e.g., apertures) 102 thatextend through the modules. In some embodiments, through holes 102 ofplurality of modules may be aligned for receiving a supporting rod 160.The support rods 160 keep the modules together and preventslipping/sliding of one module with respect to other modules.

The modular phantom 100 may also include a plurality of fasteners (e.g.,shaft collars, end plates, lids) 150 provided at opposite ends of themodular phantom 100, as illustrated in FIG. 1A. The fasteners 150 may beconfigured fix the modules in place. For example, the fasteners 150 maycouple to the support rods 160. In the exemplary embodiment illustratedin FIG. 1A, the modular phantom 100 is held together with four fasteners150 provided at a first end, and four additional fasteners 150 providedat a second, opposite, end of the phantom 100. The fasteners 150 arecoupled to four support rods 160 at each end. One of ordinary skill inthe art will understand that any number (including zero) and type ofattachment means and any number (including zero) and type of fastenersmay be used in connection with the modular phantom described herein. Theattachment means and fasteners illustrated in FIG. 1A are forillustrative purposes only and should not be interpreted as limiting.

FIGS. 1D-1E illustrate an alternative exemplary attachment means (e.g.,a peg and a hole attachment) for adjacent modules. The peg-and-holeattachment means may restrict the rotation of adjacent modules withrespect to each other while keeping the adjacent modules together.

As illustrated in FIG. 1D, a first module 156 may include a cavity 152,and a second module 158 (adjacent to the first module 150 in the modularphantom 100) may include a protrusion 154. As illustrated in FIG. 1E,the protrusion 154 of the second module 158 may be shaped anddimensioned to fit into the cavity 152 of the first module 156.Similarly, the cavity 152 of the first module 156 may be sized anddimensioned to receive the protrusion 154 of the second module 158. Whenassembled in the modular phantom 100, the protrusion 154 of the secondmodule 158 may be inserted into the cavity 152 of the first module 156,thereby attaching the second module 158 to the first module 156.

According to various embodiments, each module may include one or moreprotrusions, and one or more holes. For example, the first module 156may also include a protrusion that may couple to a cavity of a moduleprovided on an opposite side of the first module 156. Similarly, thesecond module 158 may also include a cavity that may couple to aprotrusion of a module provided on an opposite side of the second module158. This way, the modular phantom may be formed by coupling one moduleto an adjacent module. In some embodiments, the peg-and-hole attachmentmeans may be used along with other attachment means, such as one or moresupport rods.

According to various embodiments, the modular phantom may also includeone or more instruments (e.g. ionization chambers) for dosimetrymeasurement. Referring back to FIG. 1A, the modular phantom 100 mayinclude a central through hole 104 provided at the center (along acentral line) of the modular phantom 100. The plurality of through holes102 may be provided around the central through hole 104. One or more ofthe through holes 102, and/or the central through hole 104 may alsoserve as ionization chamber holes configured to receive an instrument(e.g. an ionization chamber or a similar dosimeter) for measuring thedosimetry of the medical imaging system, which is discussed below ingreater detail.

As provided above, an exemplary attachment means may include a sleeve(e.g. an annulus). FIGS. 2A-2B illustrate an exemplary sleeve 200 havinga central through hole 202 for receiving one or more of the modules ofthe modular phantom 100 therein. The sleeve 200 may have a predeterminedthickness 204 that may depend, for example, of the properties of theimaging system where the modular phantom 100 will be used. In someembodiments, the predetermined thickness 204 may depend, for example, ofthe properties of the imaging system that will be assessed using themodular phantom 100. According to various embodiments, the sleeve 200may have any shape or form. For example, the sleeve 200 may be acircular sleeve (as illustrated in FIG. 2A) or elliptical (asillustrated in FIG. 2B). In some embodiments, the sleeve 200 may be asolid sleeve. The sleeve 200 may include one or more peripheral holes.

According to various embodiments, the modular phantom (as well as eachmodule) may have any size and dimension according to the particular useof the modular phantom 100. In some embodiments, the diameter of themodular phantom 100 may be about 18 cm or less. The sleeve 200 thatenvelops the modular phantom 100 may increase an external diameter ofthe modular phantom. In some embodiments, the diameter of the sleeve 200containing the modular phantom 100 may be a size suitable for use inconnection with a CT scanner (e.g., about 32 cm). For example, for anelliptical phantom sleeve, the diameter may be 32 cm on the major axisand 24 cm on the minor axis. According to various embodiments, thesleeve 200 may be configured to keep the various modules together, whilethe sleeve may also be configured to increase the diameter of thephantom to a diameter larger than the diameter of the various modules.

The various phantom modules will be described next.

FIG. 3A illustrates a perspective view of an exemplary cone-beam module120. FIG. 3B illustrates the top view of the exemplary cone-beam module120 and FIG. 3C illustrates a side view thereof. The cone-beam module120 may include a body 300, a plurality of through holes 302 and acentral through hole 304 provided at the center (along a central line)of the body 300. The plurality of through holes 302 may be providedaround the central through hole 304 that may remain hollow or mayreceive an instrument therein. According to various embodiments, thethrough holes 302 may have a dual purpose. The plurality of throughholes 302 may form pathways for the attachment means (e.g., support rods160) and/or may receive an instrument (e.g. an ionization chamber). Thecone-beam module 120 may also include a cavity 306 adapted to receive aninsert 340 based on a medical imaging and dosimetry applicationassociated with the cone-beam module 120. The cavity 306 may extendalong a portion of the height (e.g. depth) of the cone-beam module 120.In some embodiments, the cavity 306 may extend along the entire heightof the cone-beam module 120 and may be a through hole. The details ofthe insert 340 are shown in FIGS. 3G-3J. In some embodiments, the cavity306 may have a larger diameter than the plurality of through holes 302.

The cone-beam module 120 may be used to measure a cone-beam artifact fora particular imaging system. The cone-beam artifact may refer to anerror in an image acquired with the particular imaging system. Thecone-beam artifact may be induced by discrepancies between themathematical modeling and the actual physical imaging process. Thepresence of the cone-beam artifact in an acquired image may degrade thequality of the image to a non-diagnostic level. The cone-beam module 120may be used to quantify an amplitude of the cone-beam artifact in amanner that is interpretable between various imaging and analysissystems.

As described below, the cone-beam module 120 may be placed at variouscone angles (i.e., distance from the central axial plane containing aray from the radiation source that is perpendicular to the detector ofthe imaging system) to characterize the dependence of cone-beam artifacton position in the image reconstruction. In some embodiments, thecone-beam artifact is expected to be very small/negligible in thecentral axial plane. The artifact may become more severe as thecone-beam module 120 is placed farther (in +/−z direction) from thecentral axial plane. As used herein, the x and y directions define theaxial plane (e.g., the transaxial or transverse plane). The z directionmarks the long direction of the modular phantom 100, as shown in FIG.1C.

FIG. 3B illustrates cut-out views 310 and 312 of the cone-beam module120 including the insert 340 at the cavity 306. According to the variousembodiments, the cavity 306 may be provided anywhere on the body 300 ofthe cone-beam module 120.

FIGS. 3G-3J illustrate the details of the insert 340. According toexemplary embodiments, the insert 340 may be a solid object having asmooth surface. The insert 340 may include at least two components (e.g.two discs 348, 349) stacked along a z-direction of the cone-beam module120. The components of the insert 340 may include a first portion 342and a second portion 344 that sandwich a first disc 346 provided betweentwo secondary discs 348 and 349. Thus, the insert 340 may be formed of afirst background portion (e.g. the first portion 342), a first disc(e.g. secondary disc 348), a second background portion (e.g. first disc346), a second disc (e.g. secondary disc 349), and a third backgroundportion (e.g. the second portion 342). The thickness of the backgroundportions may depend upon the particular use of the insert 340. Adiameter of the first disc 346 may be equivalent to a diameter of thefirst portion 342 and the second portion 344 of the insert 340, as wellas a diameter of the secondary disks 348 and 349. According to variousembodiments, the body 300 and/or the insert 340 of the cone-beam module120 may be made of acrylic, polycarbonate, Delrin, polyethylene, anymember of the plastic or polyurethane, Teflon. In some embodiments, thebody 300 may be made of a first material and the insert 340 may be madeof a second, different, material. For example, the body 300 may be madeof acrylic and the insert 340 may be made of Teflon.

As provided above, the cone-beam module 120 may be used to measure thecone-beam artifact for a particular imaging system. FIG. 3D illustratesan exemplary cone-beam module 120, excluding holes for support rods anddosimetry in accordance with embodiments of the invention. Asillustrated in FIG. 3D, the insert 340 including at least twodisc-shaped portions that may be inserted in the cavity 306 of thecone-beam module 120. FIG. 3E illustrates an image 314 of the cone-beammodule 120 captured in a tomographic slice (for example, a coronal orsagittal slice) that is perpendicular to the plane of the two portions342, 344 of the insert 340. One or more profiles of the image pixelvalues may be acquired as depicted by the axis 312. This profile may beone line of voxels, or a number of adjacent voxels may be averaged. FIG.3F illustrates an exemplary profile 318 corresponding to the axisillustrated in FIG. 3E. The profile 318 illustrates peaks (P) 322,valley (V) 324 and background (B) 326. The cone-beam factor (U) may bedefined as

$U = \frac{P - V}{P - B}$whereU=1 if V=B (i.e., if the pixel value of the valley equals that of thebackground), andU=0 if V=P (i.e., if the pixel value of the valley equals that of thepeak), andU has a value between 0 and 1 for values of V that are intermediate to Band P.The cone-beam factor (U) provides a quantitative measurement of themagnitude of cone-beam artifact. The cone-beam factor (U) may representthe severity of the cone-beam artifact. The cone-beam factor may bemathematically converted to a range where U spans from 0% (no cone-beamartifact) to 100%.

Another type of module used in the modular phantom 100 may be an anglededge module 170 configured to characterize at least one of a spatialresolution or contrast properties of the imaging system. The contrastproperties of the imaging system may include one or more of contrast,contrast-to-noise ratio, and the modulation transfer function (MTF) as afunction of constant of the imaging system. MTF may represent thespatial frequency response of the imaging system or a component. MTF mayrepresent the contrast at a given spatial frequency relative to lowfrequencies. FIG. 4A illustrates a perspective view of an exemplaryangled edge module 170. The angled edge module 170 may include a body400, a plurality of through holes 402 and a central through hole 404provided at the center (along a central line) of the body 400. Theplurality of through holes 402 may be provided around the centralthrough hole 404. The plurality of through holes 402 form pathways. Insome embodiments, attachment means (e.g., support rods) may be insertedinto the pathways formed by the through holes 402 to keep the modules ofthe assembled modular phantom 100 in place. One or more of the throughholes 402, and/or the central through hole 404 may receive an instrument(e.g., an ionization chamber) for dosimetry measurement, which isdiscussed below in greater detail.

According to various embodiments, the plurality of through holes 402 ofthe angled edge module 170 may be aligned with the through holes 302 ofthe cone-beam module 120. The angled edge module may also include aplurality of cavities 406. The cavity 406 may extend along a portion ofthe height (e.g. depth) of the angled edge module 170. In someembodiments, the cavity 306 may extend along the entire height of theangled edge module 170 and may be a through hole. In some embodiments,the cavities 406 may have a larger diameter than the plurality ofthrough holes 402. In other embodiments, the cavities 406 may havediameters of same or comparable size as the diameters of the throughholes 402. The plurality of cavities 406 may be dispersed along thesurface of the angled edge module 107 in an alternating manner with theplurality of through holes 402. According to various embodiments, theangled edge module 170 may also include one or more inserts 418provided, for example, in the central through hole 404, or in one ormore of the plurality of cavities 406. The inserts 418 of variouscontrast to the background material, thereby allowing measurement ofcontrast properties (e.g. contrast, contrast-to-noise ratio, and themodulation transfer function (MTF)) of the imaging system. In someembodiments, the edges of the inserts 418 may be used to measure theedge-spread function and modulation transfer function as a measurementof spatial resolution (in the axial plane). According to someembodiments, an exemplary imaging system may exhibit contrast-dependentspatial resolution, so the ability to measure the edge-spread functionfor various contrast levels may be particularly useful.

The inserts 418 may include at least one angled edge or an angledsurface that allows the measurement of the edge spread function in thedirections x, y, and/or z of the modular phantom. The edge spreadfunction may be considered to be the integral of the line-spreadfunction, and may be used to compute the modulation transfer function(MTF). According to various embodiments, the edge 414 of the insert 418of the angled edge module 170 form the basis for the edge spreadmeasurement. From the edge 414 of the insert 418, the MTF can bemeasured in the x or y directions (or any angle in the xy plane). Insome embodiments, the angled edge module 170 may be oriented in variousdirections to measure the edge spread function in x, y, or anyintermediate directions in the axial plane. In some embodiments, theangled edge module 170 may be converted to a module that presents theedge spread object (e.g., the insert 418) at an angle that is notorthogonal to the axial plane. For example, placing the edge spreadobject at 45° to the axial plane may allow measurement of the edgespread function in the z direction.

FIGS. 4B-4D show cross-sections of an exemplary modular phantomincluding at least one angled edge module 170. The modular phantom isrotated around its central axis between each cross section 430, 432 and434 illustrated in FIGS. 4B-4D, respectively. FIGS. 4B-4D illustratedifferent cross sectional views of the insert 418 provided at all fourcavities 406 of the angled edge module 170.

As illustrated in FIG. 4A, the inserts 418 may have various types ofangled edges 414. For example, the first set of inserts 410 may beinserted into the angled edge module 170 to have a flat edge 412 at afirst end (e.g., bottom) of the angled edge module 170 and an anglededge 414 at a second end (e.g., top) of the angled edge module 170. Thesecond set of inserts 416 may be inserted into the angled edge module170 to have an angled edge 415 at a first end (e.g., bottom) of theangled edge module 170 and a flat edge 413 at a second end (e.g., top)of the angled edge module 170. The first set of inserts 410 and thesecond set of inserts 160 are shown for illustrative purposes and shouldnot be viewed as limiting. In some embodiments, the inserts may be mixedand matched, and the set of inserts may have non-identical inserts. Insome embodiments, multiple inserts may be provided in the same cavity406. According to some embodiments, the edge 414 of the insert 418 maybe flat, curved, linear or non-linear.

FIGS. 4E-4H illustrate exemplary inserts 420-428 for the angled edgemodule 170. According to some embodiments, the angled edge module 170may include at least two inserts 420 and 422. As illustrated in FIG. 4E,the first insert 420 and the second insert 422 may have differentshapes, or may be inserted in the corresponding cavities 406 to form adesired shape. For example, the first insert 420 and the second insert422 may be provided to be symmetrical with respect to a central axis ofthe angled edge module 170. The first insert 420 and the second insert422 may be provided in the angled edge module 170 to be parallel to eachother. In some embodiments, one or more inserts may be identical (i.e.,may have the same shape). As illustrated in FIG. 4E, the inserts 420 and422 have a planar surface and one or more edges that are presented at apredetermined angle (e.g., 45°).

According to various embodiments, the surface of the inserts may haveany shape or form. The surfaces may be flat or curved, linear ornon-linear. FIG. 4F illustrates the angled edge module 170 with anexemplary insert 424 having an angled edge 430 presented at a givenangle with respect to the z axis 431 but the angle normal to the anglededge 430 precesses about the z axis 431 (e.g., the insert 424 is acone). According to various embodiments, the edge surface 430 may beflat, curved, or may have surface irregularities.

FIG. 4G illustrates an angled edge module 170 having an insert 426 witha series of angled edges 432 with different angles (i.e., the insert 426is a polyhedron), making the insert 426 piece-wise flat but with anglededges 432 expressed in three dimensions with a multitude of differentfacet angles.

FIG. 4H illustrates an angled edge module 170 with an insert 428 havinga smooth, curved surface 435 in three dimensions. According to variousembodiments, the surface 435 of the insert 428 may be hemispherical,elliptical, or otherwise non-planar in cross section.

According to various embodiments, the body 400 and/or the insert(s) 418of the angled edge module 170 may be made of acrylic, polycarbonate,Delrin, polyethylene, Teflon, various polyurethane mixtures, or anyplastic presenting a relatively homogeneous material that is differentfrom the background material. For example, the body 400 of the anglededge module 170 may be made of acrylic and the insert 418 may be made ofTeflon. In some embodiments, the body 400 may be made of a firstmaterial and the insert 418 may be made of a second, different,material.

According to some embodiments, the modular phantom may include two ormore angled edge modules, the insert of each of the angled edge modulesmay be made of a different material. For example the insert in the firstangled edge module may be made of Delrin, and the insert in the secondangled edge module may be made of Teflon. In some embodiments, a givenangled edge module may include more than one insert, each insert made ofdifferent material. Using inserts made of different materials (as wellas surface features, edge angles) may allow for measuring differentproperties of the MTF including characterizing the MTF at differentcontrast levels, which may be impacted by various reconstructionalgorithms.

In some embodiments, the angled edge module 170 can be used to measure(1) the contrast (i.e., the difference in average pixel value within theinsert and in the background), (2) the contrast to noise ratio (CNR),which is the contrast divided by a measure of the standard deviation inthe insert and/or background, and (3) the MTF at one or more levels ofcontrast. For various CT or cone-beam CT systems, spatial resolution maydepend on the contrast. For such systems, a “nonlinear” imagereconstruction algorithm may be used. Accordingly, an angled edge moduleconfigured to measure MTF at different levels of contrast may be usedconnection with those CT or cone-beam CT systems where the spatialresolution depends on the contrast.

Another module that may be used in connection with the modular phantom100 may be a line spread module 140. FIG. 5A illustrates a perspectiveview of an exemplary line spread module 140. FIG. 5B illustrates thetop/bottom view of the exemplary line spread module 140 and FIG. 5Cillustrates a side view thereof.

According to various embodiments, the line spread module 140 may be usedto measure line-spread function of the imaging system. The line-spreadfunction may be analyzed in terms of the modulation transfer functionfor characterization of spatial resolution of the imaging system. Insome embodiments, the line spread module 140 may be oriented in variousdirections to measure the line-spread function in the x or y direction,or intermediate directions in the axial plane. In some embodiments, theline spread module 140 may be converted to a module that presents theline spread object at an angle that is not orthogonal to the axialplane. For example, placing the line spread object at 45° to the axialplane may allow measurement of the line-spread function in the zdirection.

In some embodiments, the angled edge module 170 may be designed tomeasure the modulation transfer function (MTF) in the x, y, z, or anyintermediate directions, while the line spread module 140 may bedesigned to measure the MTF in the x, or y directions, or in anydirection in the (x, y) plane.

Referring to FIG. 5A, the line spread module 140 may include a body 500,a plurality of through holes 502 and a central through hole 504 formedin the body 500, at the center (along a central line) of the line spreadmodule 140. The plurality of through holes 502 may be provided aroundthe central through hole 504. According to various embodiments, thecentral through hole 504 may remain hollow or may receive an instrument.In some embodiments, the plurality of through holes 502 form pathwaysfor the attachment means (e.g., support rods 160) to keep the modules ofthe assembled modular phantom 100 in place. In some embodiments, theplurality of through holes 502 of the line spread module 140 may bealigned with the through holes 302 of the cone-beam module 120.

The line spread module 140 may also include a plurality of cavities 506with a larger diameter than the plurality of through holes 504. Theplurality of cavities 506 may be dispersed along the surface of the linespread module 140 in an alternating manner with the plurality of throughholes 504. The cavity 506 may extend along a portion of the height (e.g.depth) of the line spread module 140. In some embodiments, the cavity506 may extend along the entire height of the line spread module 140 andmay be a through hole. According to various embodiments, the line spreadmodule 140 may also include a plurality of 510 inserts provided in oneor more of the cavities 506. Each insert 510 may be include a slit 512that extends along a central line of the insert 510. As shown in FIG.5B, according to various embodiments, the slits 512 of the plurality ofinserts 510 may not be aligned on the surface of the line spread module140. According to various embodiments, the slit 512 is provided to forma contrast from the surrounding insert 510. In some embodiments, insteadof (or in addition to) a slit, the inserts 510 may include a thin sheetor film of material that results in a contrast from the surroundingplug.

The details of the insert 510 are shown in FIGS. 5D-5E. The insert 510may include a first component 514 and a second component 516 separatedby the slit 512 extending along a central line of the insert 510. Thefirst component 514 and the second component 516 may be stacked along ax-direction of the line spread module 140. As illustrated in FIG. 5E, atleast one of the first component 514 and the second component 516 mayinclude surface features such as protrusions 518 along the surface ofthe component. The protrusion 518 may form the slit 512 between thefirst component 514 and the second component 516.

Another type of module that may be used in connection with the modularphantom 100 described herein may be a homogenous module (e.g., a uniformmodule) 110. FIG. 6A illustrates a perspective view of an exemplaryuniform module 110. FIG. 6B illustrates a side view of uniform module110. The uniform module 110 may be used to measure the uniformity,noise, and/or noise-power spectrum (each of which is defined above)associated with the medical imaging device. In some embodiments, theuniform module 110 may be used for dosimetry assessment of the medicalimaging device. For example, the instrument for assessing the dosimetry(e.g. a dosimetry meter or the dosimetry ion chamber) may be providedwithin through holes of the uniform module 110.

The uniform module 110 may include a body 106, a plurality of throughholes 102 and a central through hole 104 formed on the body 106. Thecentral through hole 104 may be provided at the center (along a centralline) of the uniform module 110. The plurality of through holes 102 areprovided around the central through hole 104. In some embodiments, thecentral through hole 104 may remain hollow or may receive an instrumenttherein. In some embodiments, the plurality of through holes 102 may beprovided uniformly around the central through hole 104. The plurality ofthrough holes 102 form pathways for the attachment means (e.g., supportrods 160) to keep the modules of the assembled modular phantom 100 inplace. The plurality of through holes 102 of the uniform module 110 maybe aligned with the through holes 202 of the cone-beam module 120, thethrough holes 302 of the angled edge module 170, and the through holes402 of the line spread module 140.

In some embodiments, a radiation exposure meter may be inserted in oneof the through holes 102 and the central through hole 104 of the modularphantom 100. The uniform module 110 may be suitable for providing theradiation exposure meter as the uniform module 100 provides anon-perturbed medium for x-rays to reach the through holes 102 or thecentral through hole 104.

Order of the Modules in an Exemplary Assembled Phantom

A given modular phantom may include one or more modules arranged in apredetermined order that depends, in part, on characteristics of themeasurements that will be made using the phantom, geometry (e.g., focalpoint) and properties (e.g., cone angle) of the scanner, object (e.g.,body part) that is being imaged, the materials that is used for themodules, etc. The order of the modules within the phantom may alsodepend on the particular use of the phantom. For example, a phantom fora dental CT scanner may have modules arranged in an order that isdifferent than a phantom for a breast CT scanner.

According to an exemplary embodiment, the phantom may include onecone-beam module placed along the central ray of a CT scanner. Othermodules (including one or more of the cone-beam module, the angled edgemodule, the line spread module, the uniform module, and/or othermodule(s)) may be placed at a maximum cone angle available for aspecific cone-beam CT system.

It may also be necessary to include more than one of the same module inthe modular phantom depending on the desired measurements to beperformed using the modular phantom. For example, a first cone-beammodule may be provided along a central axial plane of the modularphantom where the cone angle is zero, and a second cone-beam module maybe provided at a predetermined distance (e.g., greater than 1 cm) of thecentral axial plane of the modular phantom where the cone angle is notzero.

Placement of modules at a particular cone angle may be important inaccurately characterizing a particular aspect of imaging performanceand/or examining the dependence of a particular performancecharacteristic on position in the image.

For example, the cone-beam module may be placed at various cone anglesto examine the dependence of the cone-beam artifact on position in theimage. Typically, the cone-beam artifact increases with cone angle.Similarly, the dependence of uniformity and noise on position in theimage may be investigated by positioning the uniform module at variouscone angles. Similarly, the dependence of spatial resolution on positionin the image may be investigated by placing the line spread moduleand/or the angled edge module at various cone angles. The angled edgemodule (angled edge or curved surface allowing measurement of ESF in thex or y or z directions) may be placed at various cone angles tocharacterize the dependence of spatial resolution on position in theimage. Similarly, the angled edge module may be placed at various coneangles to measure the dependence of contrast and/or CNR on position inthe image.

According to another exemplary embodiment, the phantom may include aline spread module aligned with the central ray of the CT scanner tooptimize the evaluation of spatial resolution in the (x, y) plane of theimaging system.

According to an exemplary embodiment, the phantom may include at leastone line spread module at a predetermined distance from the central rayof the CT scanner, to estimate the spatial resolution in the (x, y)plane of a practical area which would correspond to patient anatomywhere there is a finite (i.e., non-zero) cone-beam angle.

According to an exemplary embodiment, the phantom may include an anglededge module at or near the central ray of the scanner to evaluate thecontrast and gray scale consistency of the scanner at this optimallocation in the field of view.

According to an exemplary embodiment, the phantom may include one ormore of angled edge modules placed away from the central ray of thescanner where the cone angle is greater than zero degrees. The phantommay be used to evaluate how the gray scale performance of the scanner isimpacted by the non-zero cone angle. This type of phantom(s) could beplaced at multiple cone angles using multiple CT acquisitions, toevaluate a comprehensive measurement of gray scale performance as afunction of cone angle.

According to an exemplary embodiment, the phantom may include a uniformmodule at the central ray of the scanner where the cone angle approacheszero degrees. This type of phantom may be used to evaluate imageuniformity at this location in the scanner.

According to an exemplary embodiment, the phantom may include a uniformmodule located at increasing distances from the central ray of thescanner to evaluate image uniformity as a function of location (i.e.,cone angle) in the scanner.

Referring now to FIG. 7A, an exemplary phantom is illustrated with oneor more radiation measurement instruments inserted in long holes. Thephantom 700 may include a uniform module 702 positioned near the centralray of the scanner. The phantom may also include one or more instrumentssuch as a first instrument 708 inserted into a first cavity 704 and asecond instrument 710 inserted into a second cavity 706 to measureradiation levels at, for example, the uniform module 702 level.According to various embodiments, the instruments 708, 710 may be placedat other module-levels in the phantom 700.

The instruments 708, 710 may include an air ionization chamber orsimilar electronic dosimeter. The instruments may similarly includeother forms of dosimeter, such as thermoluminescent dosimeters orradiosensitive film (such as gafchromic film). The instrument(s) may beplaced (serially using multiple CT scans) in any of the cavitiesillustrated in FIG. 7A, including the second (e.g., central cavity) 706and the cavities (e.g., the first cavity 704) along the periphery of thephantom 700.

According to some embodiments, the instruments 708, 710 may communicatewith a computing device via a wired or wireless connection. Theinstruments 708, 710 may transmit the data associated with themeasurements to the computing device. The computing device may analyzethe received data, and output the data to a user. In some embodiments,the instruments 708, 710 may include a built-in memory for storing data(e.g. the result of the measurements). The data may be retrieved or readfrom the memory of the instruments 708, 710 after removing theinstruments 708, 710 from the modular phantom 700. Yet in otherembodiments, the instruments 708, 710 may include a display screen fordisplaying the result of the measurements.

In cone-beam CT dosimetry, the instrument (e.g., the ionization chamber)may be placed within one or more of the through holes in place of thesupport rods. The through hole containing the instrument may be thecenter through hole and/or one or more of the peripheral through holes.In some embodiments, the peripheral through holes may be configured toreceive the attachment means (e.g., the support rods). One or more ofthe peripheral holes may also be configured to accept an instrument(e.g., ionization chamber). In some embodiments, it may be desired to doa dose measurement at all through holes (i.e., the center through holeand all peripheral through holes). In other embodiments, it may bedesired to do a dose measurement at a subset of the through holes. Suchdose measurements may be made with the instrument positioned in thethrough hole, at the center module (e.g., halfway between the top andbottom of the phantom stack). In some embodiments, it may be desirableto obtain the dose measurement as a function of z. This may be achievedby pulling the ionization chamber from the center toward one end or theother end of the modular phantom.

Imaging System

The phantom including a plurality of modules may be imaged by acone-beam CT scanner. An exemplary medical imaging system according toembodiments is illustrated in FIGS. 7B-7C. The medical imaging system760, 762 may include a scanner that has a radiation source 750 emittingradiation (e.g., an x-ray source emitting x-rays), a detector 756 and atarget object 752 being imaged (e.g., body part or the modular phantom)placed between the radiation source 750 and the detector 756. Thecentral ray 754 is a line emitted from the radiation source 750 andgenerally striking detector 756 normally with respect to the plane ofthe detector 756. The radiation source 750 may emit the radiation (e.g.,x-rays), and the detector 756 captures the radiation (e.g., the −x-rays)that traveled through the target object 752 (e.g., the modular phantom).

As illustrated in FIG. 7C, the modular phantom 752 may be aligned withan axis of rotation 758 of the medical imaging system 762. Accordingly,the modular phantom 752 may rotate with respect to the detector 756 andthe radiation source 750 during the imaging function. Image volume dataof the target object 752 is captured at the detector 756. The imagevolume data set that is produced by that medical imaging system 760 maybe gathered and evaluated using algorithms to quantify severalperformance parameters of the medical imaging system 760 including themagnitude of the cone-beam artifact (using the cone-beam module), themodulation transfer function (MTF) (using the angled edge module),spatial resolution (using the line spread module), contrast to noise(using the angled edge module), and gray scale uniformity or homogeneity(using the uniform module).

FIG. 8 illustrates an exemplary flowchart 800 of steps that areperformed in measuring the imaging performance and dosimetry of themedical imaging system illustrated in FIG. 7B or 7C.

At step S802, one or more properties associated with an imagingperformance of the medical imaging system to be measured are determined.The properties include one or more of a spatial resolution, an imageuniformity, an image noise, a contrast to noise ratio, or a cone-beamartifact associated with the medical imaging system. The step may alsoinclude determining the plurality of modules that will be incorporatedin the modular phantom. The plurality of modules may include one or moreof a cone-beam module, a line spread module, an angled edge module, anda uniform module.

At step S804, a predetermined order of the plurality of phantoms isidentified based on the one or more properties to be measured. Thepredetermined order may be changed as necessary, modules may be moved upand down, modules may be removed, or additional modules may be added asdesired. The types of the modules to be included in the phantom and theorder of the modules may also be determined based on the type of scanner(e.g., dental imaging, breast imaging, etc.) in addition to thecharacteristics of the scanner that needs to be determined/measured.

At step S806, the phantom may be assembled to include the plurality ofmodules in the predetermined order.

At step S808, the assembled modular phantom may be placed between adetector and a radiation source of the medical imaging system. Forexample, at least one of the plurality of modules may be aligned with acentral ray of the medical imaging system. The medical imaging system(e.g., a CT scanner) may be operated such that the source of theradiation source of the medical imaging system emits radiation (e.g.,X-rays) through the modular phantom.

At S810, the detector may collect/capture the X-rays that traveledthrough the phantom that, when acquired as a sequence of images over anangular coverage, are used to reconstruct an image volume data set.Thus, image volume data of the phantom may be produced when the dataacquired by the detector are reconstructed.

At S812, the image volume data captured on the detector may be analyzedaccording to one or more of the algorithms to determine imagingperformance and dosimetry of the scanner. For example, the image volumedata may be analyzed to measure the one or more properties associatedwith the imaging performance of the medical imaging system and thedosimetry of the medical imaging system. The measurement of the imagingperformance and the dosimetry may be made concurrently or subsequentlyto each other. According to various embodiments, measurement of theimaging performance and the dosimetry may be made using the sametechnique factors. Thus, in some embodiments, multiple measurements maybe performed using the same modular phantom.

The results of the analysis may be used to assess properties of the CTscanner and, if necessary, to calibrate the CT scanner.

According to various embodiments, the modular phantom may be used tocompare multiple medical imaging systems (e.g., CT scanners). Forexample, an exemplary phantom including a predetermined set of modulesassembled according to a predetermined order may be aligned with a firstmedical imaging system. Imaging performance and dosimetry of the firstmedical imaging system may be determined as discussed above inconnection with FIG. 9 . Thereafter, the same exemplary phantom may bealigned with a second medical imaging system. Imaging performance anddosimetry of the second medical imaging system may be determined asdiscussed above in connection with FIG. 9 . The imaging performance anddosimetry of the two medical imaging systems may be compared to compareand/or calibrate the two medical imaging systems.

The imaging system may include a computer apparatus (e.g., a servercomputer) including one or more processors and a memory storinginstructions to execute the algorithms. The computer apparatus may becoupled using wire or wirelessly to the CT scanner. For example, thecomputer apparatus may be coupled to the detector of the scanner toreceive image data from the detector. An image volume data set isproduced through reconstruction of two or more projection images. Insome embodiments, the computer apparatus may also be coupled to thesource so as to control (e.g., activate and deactivate) the source.

A portion of the subsystems or components of an exemplary computerapparatus are shown in FIG. 9 . The subsystems shown in FIG. 9 areinterconnected via a system bus 905. The subsystems such as a printer904, keyboard 905, fixed disk 909 (or other memory comprisingcomputer-readable media), monitor 906, which is coupled to a displayadapter 912, and others are shown. Peripherals and input/output (I/O)devices, which couple to I/O controller 901, can be connected to thecomputer system by any number of means known in the art, such as serialport 907. For example, serial port 907 or external interface 910 can beused to connect the computer apparatus to a wide area network such asthe Internet, a mouse input device, or a scanner. The interconnectionvia system bus allows the central processor 903 to communicate with eachsubsystem and to control the execution of instructions from systemmemory 902 or the fixed disk 909, as well as the exchange of informationbetween subsystems. The system memory 902 and/or the fixed disk 909 mayembody computer-readable medium. The computer system described herein isthen used to perform analysis of the images produced of the phantom bythe cone-beam CT system.

Assessment Algorithm(s)

According to various embodiments, the algorithms may include executionon a parallel processor, such as a graphics processing unit (GPU), fordetermining image performance metrics using algorithms.

According to various embodiments, the algorithm for determination ofspatial resolution could be designed to characterize the edge spreadfunction (ESF) using the angled edge module (the edge of tomulti-faceted or curved surface of the angled edge module) orline-spread function (LSF) using the line spread module. The algorithmmay then compute the Modulation Transfer Function from the LSF data, aswell as the full width at half maximum (FWHM) of the LSF.

An embodiment of the algorithm operates on the images of the cone-beammodule to estimate the contrast of the central region relative to theimages of the two disks that are included in the cone-beam module. Therelative contrast identified using the cone-beam modules enables toquantify the cone beam artifact for the imaging system.

Another embodiment of the algorithm operates on image data correspondingto the uniform module, and assesses a profile across this region whichaverages a line of image data encompassing from 1 pixel wide up to 100pixels wide. The algorithm is designed to avoid the air holes in thephantom module.

Another embodiment of the algorithm computes the average gray scale nearthe center of the uniform phantom avoiding the air hole in a circular orsquare (or other appropriate shape) region of interest (ROI, ROIc forthe central ROI) and also computes the average gray scale in one or moreROIs near the periphery of the phantom—and the peripheral ROI data isaveraged (ROIp), and compared to the mean gray scale near the phantomcenter. The uniformity of the scanner can be quantified using metricssuch as ROIc-ROIp and other simple mathematical combinations of thesemetrics.

Measurements of Dose Metrics and Image Performance Metrics

Phantoms according to various embodiments discussed herein may measurethe imaging performance and the dosimetry of a medical imaging system(e.g., a CT scanner) using the same technique factors of the medicalimaging system. The technique factors may include one or more of a tubepotential, a tube current, a time of exposure, and a system geometry(e.g., a field of view (FOV) of the imaging system, asource-axis-distance (SAD) of the imaging system, asource-detector-distance (SDD), and an extent of the source-detectororbit) of the medical imaging system.

The phantoms may measure the air ionization levels (such as air kineticenergy released per unit mass (i.e., air kerma) or exposure) in thecentral and peripheral through-holes of the modules, and combine the airionization levels to calculate Ko=a×Kc+(1−a) Kp, where Ko is a doserelated metric, Kc is the air kerma at the center hold, Kp is the airkerma averaged across one or more peripheral holes, and a is a numberbetween 0.01 and 0.99.

An important metric determined by the phantom user (and the algorithmdescribed herein) is to assess the imaging performance (e.g., noise,noise variance, or noise power spectrum) in the uniform module (oruniform areas of the other modules) when the dose metric Ko was measuredfrom the same cone-beam CT scan. The dose can also be measured using thesame technique factors for the medical imaging device with the dosemetric (Kp) in one or more peripheral through holes of the modularphantom.

Embodiments provide a number of advantages over prior systems.Embodiments provide new and unique modules (e.g. the cone-beam module,the edge spread module, the line spread module) that, when incorporatedin a modular phantom, measure imaging performance and the dosimetry ofthe imaging system using the same technique factors. Moreover,embodiments provide phantoms that perform a range of imaging performancemeasurements. The phantoms described herein are configurable in a mannersuitable to a broad range of cone-beam CT scanner configurations. Inaddition, the phantoms described herein are consistent with emergingstandards for physical measurements for cone-beam CT accreditation in anumber of ways, including configurable overall dimensions (diameter andlength) with use of a sleeve. Embodiments further enable calibration ofthe medical imaging devices, as described above.

Specific details regarding some of the above-described aspects areprovided above. The specific details of the specific aspects may becombined in any suitable manner without departing from the spirit andscope of embodiments of the invention.

Storage media and computer readable media for containing code, orportions of code, may include any appropriate media known or used in theart, including storage media and communication media, such as but notlimited to volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage and/or transmissionof information such as computer readable instructions, data structures,program modules, or other data, including RAM, ROM, EEPROM, flash memoryor other memory technology, CD-ROM, digital versatile disk (DVD) orother optical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, data signals, datatransmissions, or any other medium which may be used to store ortransmit the desired information and which may be accessed by thecomputer. Based on the disclosure and teachings provided herein, aperson of ordinary skill in the art may appreciate other ways and/ormethods to implement the various embodiments.

It may be understood that the present invention as described above maybe implemented in the form of control logic using computer software in amodular or integrated manner. Based on the disclosure and teachingsprovided herein, a person of ordinary skill in the art may know andappreciate other ways and/or methods to implement the present inventionusing hardware and a combination of hardware and software.

Any of the software components or functions described in thisapplication, may be implemented as software code to be executed by oneor more processors and or co-processors using any suitable computerlanguage such as, for example, Java, C++ or Perl using, for example,conventional or object-oriented techniques. The software code may bestored as a series of instructions, or commands on a computer readablemedium, such as a random-access memory (RAM), a read only memory (ROM),a magnetic medium such as a hard-drive or a floppy disk, a solid statehard drive, or an optical medium such as a CD-ROM. Any such computerreadable medium may reside on or within a single computationalapparatus, and may be present on or within different computationalapparatuses within a system or network. The use of web-based softwarefor phantom image analysis is also explicitly included in thisdescription.

The above description is illustrative and is not restrictive. Manyvariations of the invention may become apparent to those skilled in theart upon review of the disclosure. The scope of the invention may,therefore, be determined not with reference to the above description,but instead may be determined with reference to the pending claims alongwith their full scope or equivalents.

One or more features from any embodiment may be combined with one ormore features of any other embodiment without departing from the scopeof the invention.

A recitation of “a”, “an” or “the” is intended to mean “one or more”unless specifically indicated to the contrary.

What is claimed is:
 1. A modular phantom for medical imaging comprising:one or more modules ordered according to a predetermined order, the oneor more modules including at least one of a cone-beam module configuredto measure a cone-beam artifact for a medical imaging system, an anglededge module configured to measure at least one of a spatial resolutionor contrast properties of the medical imaging system, or a line spreadmodule configured to measure a line-spread function of the medicalimaging system, wherein the angled edge module includes at least onecavity, and an insert provided in the at least one cavity, wherein theinsert has at least one angled edge, and wherein the insert and theangled edge module are made of different materials; wherein the modularphantom is configured to measure an imaging performance of the medicalimaging system.
 2. The modular phantom of claim 1, wherein the modularphantom comprises two or more modules, and attachment means forattaching the two or more modules, wherein the attachment means alignthe two or more modules, the attachment means includes at least onesupporting rod, wherein each module includes at least one through holeextending through the module, and wherein through holes of plurality ofmodules are aligned for receiving the at least one supporting rod. 3.The modular phantom of claim 1, further comprising a sleeve configuredto envelop the one or more modules.
 4. The modular phantom of claim 1,wherein the modular phantom includes at least two of a same module. 5.The modular phantom of claim 1, further comprising: a first cone-beammodule provided along a central axial plane the modular phantom where acone angle is zero; and a second cone-beam module provided at apredetermined distance of the central axial plane of the modular phantomwhere the cone angle is not zero.
 6. The modular phantom of claim 1,wherein at least one of the cone-beam module or the line spread moduleincludes a cavity adapted to receive an insert configured to measure theimaging performance of the medical imaging system, wherein the insertand a module comprising the insert are made of different materials. 7.The modular phantom of claim 1, wherein the one or more modules includesthe cone-beam module, and wherein the cone-beam module includes at leastone cavity, and an insert provided in the at least one cavity, whereinthe insert and the cone-beam module are made of different materials,wherein the insert includes at least two components stacked along az-direction of the cone-beam module.
 8. The modular phantom of claim 1,wherein the one or more modules includes the line spread module, andwherein the line spread module includes at least one cavity, and aninsert provided in the at least one cavity, wherein the insert and theline spread module are made of different materials, and the insertincludes a slit extending along a central line of the insert.
 9. Themodular phantom of claim 1, further comprising at least one homogenousmodule.
 10. The modular phantom of claim 1, further comprising: one ormore through holes configured to receive one or more instruments formeasuring a dosimetry of the medical imaging system; and the one or moreinstruments include an ionization chamber.
 11. The modular phantom ofclaim 10, wherein the imaging performance and the dosimetry of themedical imaging system are measured using a same set of techniquefactors for the medical imaging system, wherein the same set oftechnique factors include one or more of an exposure time, a tubepotential, a tube current, and a system geometry of the medical imagingsystem.
 12. A medical imaging system comprising: a radiation sourceconfigured to emit x-rays; a detector; and a modular phantom placedbetween the radiation source and the detector, wherein the modularphantom includes one or more modules ordered according to apredetermined order, the one or more modules including at least one of acone-beam module configured to measure a cone-beam artifact for themedical imaging system, an angled edge module configured to measure atleast one of a spatial resolution or contrast properties of the medicalimaging system, or a line spread module configured to measure aline-spread function of the medical imaging system, wherein the anglededge module includes at least one cavity, and an insert provided in theat least one cavity, wherein the insert has at least one angled edge,and wherein the insert and the angled edge module are made of differentmaterials, wherein the x-rays emitted from the radiation source travelthrough the modular phantom before being received at the detector.
 13. Amethod for measuring properties associated with a medical imaging systemusing a modular phantom including one or more modules ordered accordingto a predetermined order, the one or more modules including at least oneof a cone-beam module configured to measure a cone-beam artifact for themedical imaging system, an angled edge module configured to measure atleast one of a spatial resolution or contrast properties of the medicalimaging system, or a line spread module configured to measure aline-spread function of the medical imaging system, wherein the anglededge module includes at least one cavity, and an insert provided in theat least one cavity, wherein the insert has at least one angled edge,and wherein the insert and the angled edge module are made of differentmaterials, the method comprising: determining one or more propertiesassociated with an imaging performance of the medical imaging system tobe measured; identifying the predetermined order of the one or moremodules based on the one or more properties to be measured; assemblingthe modular phantom based on the predetermined order; placing themodular phantom between a detector and a radiation source of the medicalimaging system; collecting a first set of rays that are emitted from theradiation source on the detector after the first set of rays travelthrough the modular phantom; and measuring the one or more propertiesassociated with the imaging performance of the medical imaging systemusing the collected first set of rays.
 14. The method of claim 13,wherein measuring the one or more properties associated with the medicalimaging system includes: measuring dosimetry of the medical imagingsystem using the collected first set of rays; or measuring one or moreof the spatial resolution, an image uniformity, an image noise, acontrast, a contrast-to-noise ratio, or the cone-beam artifactassociated with the medical imaging system.
 15. The method of claim 13,wherein placing the modular phantom between the detector and theradiation source comprises: aligning at least one of the one or moremodules with a central ray of the medical imaging system.
 16. The methodof claim 13, further comprising: removing the modular phantom from themedical imaging system; assembling the modular phantom based on adifferent predetermined order into a modified modular phantom; placingthe modified modular phantom between the detector and the radiationsource of the medical imaging system; collecting a second set of raysthat are emitted from the radiation source on the detector after thesecond set of rays travel through the modified modular phantom;measuring the one or more properties associated with the imagingperformance of the medical imaging system using the collected second setof rays; and measuring dosimetry of the medical imaging system using thecollected second set of rays.
 17. The method of claim 16, wherein themodified modular phantom includes at least one module in addition to theone or more modules previously included in the modular phantom.
 18. Themethod of claim 16, wherein the modular phantom includes two or moremodules, and the modified modular phantom includes at least one moduleless than the two or more modules previously included in the modularphantom.
 19. A modular phantom for medical imaging comprising: two ormore modules ordered according to a predetermined order, the two or moremodules including at least one cone-beam module configured to measure acone-beam artifact for a medical imaging system, and at least one of anangled edge module configured to measure at least one of a spatialresolution or contrast properties of the medical imaging system, or aline spread module configured to measure a line-spread function of themedical imaging system; wherein the modular phantom is configured tomeasure an imaging performance of the medical imaging system.
 20. Amodular phantom for medical imaging comprising: two or more modulesordered according to a predetermined order, the two or more modulesincluding at least one line-spread module configured to measure aline-spread function of a medical imaging system, and at least one of anangled edge module configured to measure at least one of a spatialresolution or contrast properties of the medical imaging system, or acone-beam module configured to measure a cone-beam artifact for themedical imaging system; wherein the modular phantom is configured tomeasure an imaging performance of the medical imaging system.
 21. Amethod for measuring properties associated with a medical imaging systemusing a modular phantom including one or more modules ordered accordingto a predetermined order, the one or more modules including at least oneof a cone-beam module configured to measure a cone-beam artifact for themedical imaging system, an angled edge module configured to measure atleast one of a spatial resolution or contrast properties of the medicalimaging system, or a line spread module configured to measure aline-spread function of the medical imaging system, the methodcomprising: determining one or more properties associated with animaging performance of the medical imaging system to be measured;identifying the predetermined order of the one or more modules based onthe one or more properties to be measured; assembling the modularphantom based on the predetermined order; placing the modular phantombetween a detector and a radiation source of the medical imaging system;collecting a first set of rays that are emitted from the radiationsource on the detector after the first set of rays travel through themodular phantom; measuring the one or more properties associated withthe imaging performance of the medical imaging system using thecollected first set of rays; removing the modular phantom from themedical imaging system; assembling the modular phantom based on adifferent predetermined order into a modified modular phantom; placingthe modified modular phantom between the detector and the radiationsource of the medical imaging system; collecting a second set of raysthat are emitted from the radiation source on the detector after thesecond set of rays travel through the modified modular phantom;measuring the one or more properties associated with the imagingperformance of the medical imaging system using the collected second setof rays; and measuring dosimetry of the medical imaging system using thecollected second set of rays.